Treatment of tobacco



Feb 2 1943 J. M. MosELEY ETAL 2,3'975- TREATMENT oF ToBAcco Filed May e, 1942 Patented Feb. 2, 1943 UNITED STATES PATENT OFFICE TREATMENT or TOBACCO John M. Moseley, Richmond, and Richard Page Hudson, Hanover County, Va., assgnors to The I American Tobacco Company, New York, N. Y., a corporation of New Jersey Application May s, 1942,'seria1 N5. 441,898

5 claims. '(01. 1st-14o) This invention relates to a process for the treatment of air cured tobacco used in the manufacture of cigarettes and is a continuation in part of our copending application Serial No'. 384,738 led March 22, 1941.

. One type of cigarette extensively used in the United States at the present time is formed of a blend of Bright tobacco which is flue cured and Burley and Maryland tobaccos which are air cured. The flue cured tobacco and air cured tobaccos possess individual characteristics which give each a distinct role in determining the nature of the final blend. Bright tobacco is naturally high in carbohydrates and low in nitrogen. The high carbohydrate content of Bright tobacco is essential to two very highly valued characteristics of this type. The first of these is its flexibility resulting from a pronounced affinity for water and the second is the production of volatile acids on burning. The light color of this type of tobacco is also highly desirable because it lends attractiveness to the nal product.

The entire process of treating Bright tobacc is therefore designed to develop and maintain maximum color, sugar content and hygroscopic properties. To obtain this end the tobacco is processed in such manner that activity within the leaf is arrested as soon as these maxima are obtained. In the flue curing process commonly applied to this type of tobacco, temperatures of from 190 to 200 F. are employed as the leaf approaches the end of the rst stage of curing.

This is commonly known as setting the color. It also stabilizes the carbohydrate content and moisture holding properties. At this temperature the plant enzymes are destroyed and further changes in the composition of the leaf are largely prevented.

The air cured tobaccos used in manufacture of cigarettes of the type referred to are valued for characteristics which are quite different from those of Bright tobacco. In addition to their characteristic aromas, these types burn to form smoke which is basic in character and tends to counter-balance the acids developed from the Bright tobacco. The further important quality is their excellent ability to hold re. These types of tobacco are naturally high in nitrogen, low in carbohydrates and moisture holding ability and somewhat darker in color than the Bright type. In curing and processing the air cured tobaccos, brightness of color is sacrificedV in the development of taste and burning quality. Soluble carbohydrates are completely eliminated and moisture holding properties are seriously impaired.

The rst stage of curing of tobacco leaves consists of a starvation period during which the cells us'eup reserve plant food. Among other important changes, the starches are converted to sugar and chlorophyll is destroyed, the leaf becoming bright yellow in color. The end of the first stage of curing marks the end of the life process. Further changes are entirely chemical in nature and depend upon the natural enzymes of the leaf and Oxygen of the air. Burley and Maryland tobacco are cured on the stalk by a slow process at vatmospheric temperatures during 1 which the life process is continued in the mid- -cured.by the farmer in the manner described above, it is purchased by the cigarette manufacturer. Its moisture content is then readjusted by redrying and the tobacco is aged for one and a half to three years before use. In ageing, the

' tobacco isl encased in hogsheads at carefully regulated moisture content without access of air. The enzymes Vnaturally present in the leaf continue to function but the products of decomposition are held in the leaf. Whereas, in curing, the combined effect of evaporation of the Volatile matter in the surrounding air and translocation of soluble matter into the stalk of the plant effects a loss of 12 to 2O percent of the dry weight of the leaf web, the products of decomposition during ageing are held to such a degree that no measurable decrease in dry Weight takes place over a period of many months. The cured and aged air cured tobaccos used in the manufacture of cigarettes contain compounds which are stable and which are considered beneficial to Vsmoking quality. 'Ihey also contain less stable compounds which are detrimental in their eiect. These latter, if gaseous, are largely disseminated into the surrounding air but some are retained by absorption, adsorption and by loose'chemical combination in which state they are easily separated and disposed of. If not removed, these compounds are readily transmitted to the smoke stream and upon reaching the sensory organ of the smoker, create irritation and unpleasant taste. The free or loosely .bound products in properly aged tobacco are largely responsible for that character of smoke which is known as harshness. c.

I-Ieretofore some of these compounds have been removed from the tobacco by treatment With heated air in an apron or textile dryer. As the air cured tobaccos are low in carbohydrates and moisture holding ability, they are cased before the nal manufacture into cigarettes. This operation involves immersing in a liquid which is essdntially a solution of sugar whereby cfarbohydrates, which are essential to smoking tobacco products, are supplied to the air cured types. The tobacco in leaf form is treated with a casing solution whereby its moisture content is increased through the tobacco, then through opening I6 at the top of the partition into the space I5.

Section of the dryer, which is an intermediate section of which several may be employed in the actual drying apparatus, is similar to the section 4 except that in place of the steam pipes I3, arranged beneath the belt 9, it is provided with a similar set of closed steam pipes I1 arranged above the belt, and the air ows in the opposite direction, as indicated.

Section 6 of the dryer, which represents the las-t drying section, is also provided with closed to about 50 percent. It is then passed through a multi-section dryer to reduce the moisture content and to remove the unstable harmful constituents. In practicing the present process we introduce superheated steam into one of the sections of the dryer wlierein the treatment with superheated steam takes place after the moisture content of the tobacco has been reduced to about percent. The casing materials Which have been applied to the tobacco prior to this treatment serve as a xative for the desirable aromatic and flavoring constituents of the tobaccoand also inhibit the removal of nicotine other than that which occurs in loosely combined form as a result of the ageing reactions. The proportion of nicotine thus removed is a very small percentage of the total, rarely exceeding 5 percent of the quantity present in air cured tobacco so processed. This is not true, however, of ammonia and other compounds which contribute to harshness of which a much greater proportional amount is removed.

The process may be applied in any modern apron type drying machine capable of maintaining the proper temperatures with relatively simple modification. In the accompanying drawing we have diagrammatically illustrated apparatus suitable for use in practicing the process. In this showing:

Fig. 1 is a longitudinal, sectional View of an apron dryer showing the invention applied;

Fig. 2 is a transverse, vertical, sectional view on line 2-2 of Fig. 1; and

Fig. 3 is a similar view on line 3 3 of Fig. l.

Referring to the drawing, the dryer consists of an outer casing I divided by transverse partitions 2-3 into a plurality of compartments 4, 5 and 6. Beyond the last drying compartment 6 an open section 'I is providedfor cooling the tobacco and beyond the cooling compartment the dryer is provided with an ordering compartment 8. A belt or apron 9 passes through the entire dryer traveling over a roller I0 at the inlet end of the machine and a similar roller II at the opposite end of the machine. The ends of the dryer sections and the partitions 2 3 are provided with suitable openings for the passage of this apron.

A longitudinally extending partition I2 is arranged in the drying sections as shown in Figs. 2 andy 3 of the drawing. In the section 4, which is the first section of the dryer, we provide a series of steam pipes I3 through which steam is circulated. Adjacent the bottom of the dryer section the partition I2 is providedwith one or more openings, in which fans I4 are arranged. These fans are adapted to circulate air through the dryer section as indicated by the arrows, the air passing upwardly over the steam pipes I3,

`steam pipes I8k above the belt and is further provided with a steam pipe I9 preferably arranged near the top'oi the drying section and provided with a vplurality of perforations 20 to deliver superheated steam into the drying section. One

"or morey of the drying sections is also provided with .an outlet 5. An exhaust fan (not shown) may be arranged in this outlet to facilitate the withdrawal of air and gases from the drying chambers.

The cooling section 'I of the dryer is open to permit access of air at room temperature to the tobacco for cooling.

A water pan or container 8 is Ypla/ced in the bottom of the ordering section to supply moisture to the atmosphere of this section for ordering the tobacco. Suitable heating means may be provided for the water, if desired.

In practicing the process, the cased tobacco, which in practice generally consists of a mixture of Burley and Maryland tobaccos, is placed upon the apron 9 at the inlet end of the machine. Due to the treatment of the tobacco with the casing solution,- its moisture content at this point is approximately 50 percent. The tobacco then passes through the drying sections 4, 5 and 6. In the drying sections air is circulated by the fans I4, the air being drawn into the machine at the front through the openings provided for the passage of the apron and at other points. In passing over the coils or pipes I3 in the compartment l, this air is heated and is then passed through the tobacco on the apron 9.

Temperatures up to 270 F. are employed in the preliminary drying sections, in which the tobacco loses moisture content from its original walue of about 50 percent to about 10 percent.

In the last drying section or sections the regular steam coils for heating and fans for circulating the air are provided, and in addition superheated steam is introduced, which serves as the main instrument for thorough removal of the loosely bound compounds. A minimum of 270 F. is necessary for most eiiicient removal, but temperatures above 300 F. tend to modify the more stable compounds with -corresponding detriment of quality. Also, temperatures above 300 F. denature the colloids of leaf tissue with the result that subsequent ordering or addition of the proper amount of moisture becomes difficult or impossible. Steam is introduced into the chamber from pounds line pressure in the proportion of about 25-75 pounds of steam to 100 pounds of tobacco. This steam is initially at a temperature of 330 F.; however, heat losses in the compartment are such that additional heat is required from the heating coils to maintain a temperature of 27 0 to 300 F. The volume occupied by the steam at atmospheric -pressure and at the temperatures used is such that there is a complete change of atmosphere approximately 15-45 times an hour. Control of quantity of steam and duration of treatment may be altered according to the needs of a particular crop of tobacco. In practice we have found 4 5 minutes treatment in the compartment 6 to 4be optimum for cigarette grades of Burley and Maryland. In the drawing we have illustrated the steam introduced in the last compartment of the dryer. This arrangement may be varied, particularly in dryers comprising more than three 1compartments but in any case the steam is introduced in the compartment Where the moisture content of the tobacco is about 10 percent.

While the steam may be introduced in many diierent ways, the particular system illustrated will be explained. Referring to the drawing, steam pipe I9, having perforations 20, is connected to a feed ypipe 2|, having a hand valve 22 therein. A supply pipe 23 communicates with the pipe 2|. This pipe is preferably connected to a new meter 24 by pipes 25 and 26 arranged on opposites of an orifice plate 21. Condensers 28 are arranged in the pipes 24 and 25, and a condensate trap 29 isconnected to the lower end of the supply line 23. A pipe 30 connected to the trap communicates with the return line.

In effect the above is merely one means of introducing a Imeasured amount of steam, free from entrained moisture, into the drying chamber with provision for maintaining a predetermined temperature therein regardless of demands `for heat which would otherwise cool the steam to a saturated condition, at which point condensation would occur. Other mechanical arrangements to effect these results will readily occur to those skilled in the art.

In addition to removal of products of degenerative chemical action there has been noticed an improvement ofuniformity in drying and the practical elimination of incidental undried or wet spots. 'Ihis is -due to the higher specific heat of steam in this condition than that of air at the same temperature. It is obvious that since wet tobacco tends by evaporation to reach the wet bulb temperature of the surrounding atmosphere, and its absorption of heat is proportional to the square of temperature difference between it and the surrounding atmosphere, a higher specic heat of surrounding atmosphere allows more transfer of heat for drying :and therefore more thorough drying of such Wet spots.

Physical measurements of the leaf characteristics reveal a definite superiority of our process over the older methods of drying with air to a substantially moisture-free condition. These measurements embrace the aforementioned qualities of strength, color, resilience and hygroscopic or moisture-holding properties. Complete processing with superheated steam is not advantageous since the moisture -content of the leaf, above which impairment to the physical properties occurs with the admission of superheated steam, appears to be very critical,

Chemical analyses of tobacco and tobacco smoke have shown that the fair-superheated steam cycle as described approaches the conditions of most eiective separation of volatile irritants of tobacco from the desirable elements of flavor.

We claim:

l. The process of treating cased and aged, air cured tobacco which comprises reducing the moisture content of the tobacco to approximately 10 percent by treating the tobacco with air at a temperature of 270 to 300 F., and then treating the tobacco with heated air and superheated steam at a temperature of 270 to 300 F.

2. The process of treating cased and aged, air cured tobacco which comprises reducing the moisture content of the tobacco to approximately 10 percent by treating the tobacco with air at a temperature of 2'70 to 300 and then treating the tobacco with heated air and superheated steam Iat a temperature of 270 to 300 F. for a period of approximately 4 to 5 minutes.

3. The process of treating cased and aged, air cured tobacco which comprises reducing the moisture content of the tobacco to approximately l0 percent by treating the tobacco with air at a temperature of 270 to 300 F., and then treating the tobacco with heated air and superheated steam at a temperature of 270 to 300 F., the superheated steam being employed in the sproportion of 25 to 75 pounds of steam to 100 pounds of tobacco.

4. The process of treating a blend of cured and aged Burley and Maryland tobaccos which comprises treating the tobacco with a casing solution, the tobacco having a moisture content of about percent after such treatment, drying the tobacco with air at a temperature of 270 to 300 F. to reduce its moisture content to approximately 10 percent, and then drying the tobacco with air and superheated steam at a temperature of 270 to 300 F.

5. The process of treating :a blend of cured and aged Burley and Maryland tobaccos which com prises treating the tobacco with a casing solution, the tobacco having a moisture content of about 50 percent after such treatment, drying the tobacco with air at a temperature of 270 to 300 F. to reduce its moisture ycontent to approximately 10 percent, then drying the tobacco with air and superheated steam at a temperature of 270 to 300 F., and then treating the tobacco with wet steam to raise its moisture content to a desired point.

JOHN M. MOSELEY. RICHARD PAGE HUDSON. 

